Dear Meggie,The House Sparrows are in huge numbers in my backyard. They are very aggressive birds and will take over all the cavity nesting spots. They are kind of "mean" to other birds. I think the large population of Cardinals this year is actually helping keep the House Sparrows in check. I do see the Doves and Sparrows being caught by the Hawks too.Hard to say why their population has diminished in Australia and New Zealand. I heard their numbers were down in England as well. Maybe they are susceptible to the avian flu. Sherry